1. Field of the Invention
This invention relates to a suspension system for a vehicle, and in particular to an active suspension system.
2. Description of the Related Art
A conventional active suspension system is disclosed in, for example, Japanese Patent Laid-Open No. 62-96113 laid open to the public on May. 2, 1987, European Patent Application laid open to the public on Aug. 1, 1984 under a publication number 0114757 and U.S. Pat. No. 4,371,182 issued on Feb. 1, 1983. In the active suspension as disclosed in the publication enumerated above, a cylinder device is provided for each vehicle wheel member between a vehicle body member and a vehicle wheel member. By controlling the fluid supply/discharge to/from the cylinder device, the fluid in the cylinder device can be changed so that the vehicle suspension characteristics are changed.
In the active suspension system, the fluid pressure of each cylinder device is sensed, and the warping of the vehicle body is computed based on the sensed pressures. Then the fluid supply/discharge to/from the individual cylinder devices is controlled so as to suppress the warping of the vehicle body (hereinafter called warp control).
In the warp control, since the fluid supply/discharge to/from the cylinder devices of the front wheels is as same as that to/from the cylinder devices of the rear wheels, the warp control is not performed suitably under certain vehicle running conditions.